Method of making stable vinyl resins



Patented Oct. 7, 1941 kernel) or 2.258.410 MAKING s'rsnu: vrmu. mssms Joseph Dahlc, Springfield, Mass, assignor to Monunto Chemical Company, St. Louis, Mo., a

corporation of Delaware No Drawing. Continuation of application Serial No. 122,575, January 27, 1937. This application June 20, 1939, Serial No. 280,125

15 Claims.

I invention'relates tolvinyl acetal resins of the kind described in the patent to Morrison et ll. nopaoaaoaz, dated March 31, 1936, and a French patent to Carbide 8: Carbon Chemicals.

-ing the reactions in a single stage with an acid catalyst.

The first major step in the stabilization process is the neutralization oi the acid catalyst remaining in the solution. In the preferred practice oi! the invention a suitable alkali or alkaline salt is added to the solution in which the resin has been produced to neutralize the particular acid catalyst which has been employed and the procedure wltha non-solvent, such as water, while the solua kettle and a non-solvent tor the resin, such as water, containing about 10 to 20% of alcohol, or other lower aliphatic alcohol, such as methyl or ethyl alcohol, is added. This completes the step Corporation,'No.1.'l92,861, published January 1'7, 5' of neutralizing the acid catalyst in solution.

r1936; These resinsiareuseiul for many purposes, It the solvent is acetic acid, a water solution particularly infth'e manutacturepoi plastics and of sodium or potassium acetate containing acetic 101'; sandwich'layersior glass. Howacid, preferably. quivalent to th concentration everadmcuny nss been {experienced owing to of the acetic acid in the resin solution is then lack oistability whichmanii'ests itself by loss oi added to the resin solution. The quantity of Isolubilityand,by'disccloration'when subiectedto sodium or potassium acetate added should be e; This lack t bility has been a serious more than equivalent to the mineral acid present. in these resins and hasgreatly diminished The resin then is precipitated from the resin qtheirntillty. i v M i solution, preferably, by diluting the solution with .w .1 have discovered amethod for stabilizing these water while the solution is stirred vigorously ;:and' have produced, stable resins of this thereby precipitating the resin in small particles. type which are very much more useful than The precipitated resin is then washed with water resins heretofore produced. My present invenuntil it containsnot more than and, preferably, tion, therefore, includes my novel resin and the less than 1% acetic acid. The precipitated and process oi. making it. The resin to be treated in washed resin is then placed in a kettle in a water accordance with the present invention may be suspension containing 10 to 20% of ethyl alcohol. formed either (1) by producing polyvinyl alcohol From this point the treatment 0! the resin is by the action of an acid or alkaline catalyst and the same regardless of the type of solvent which then converting with an aldehyde to an acetal was present in'the solution in which the resinwas by the action of an acid catalyst, or (2) conductproduced.

Th second major step is neutralization while in suspension. According y, to the finely divided resin in suspension in water containing 10 to 20% alcohol is added an alkali, such as sodium or potassium hydroxide or carbonate, in amount up to about 0.2% or the weight of the batch. The

tion is stirred vigorously thereby precipitating the resin and disintegrating. it in small particles.

The surplus liquid is then drained from the premixture is heated at a temperature of from 60 to 80 0., preferably, for about two to ten hours. The time required for the treatment may will vary somewhat depending upon the. solvent 5 be shortened by the use of a higher temperapresent in the resin solution. ture or by increasing the alcoholic strength of I! the solvent is an alcohol, or other lower alithe mixture. It the quantity oi alkali added is phatic alcohol, such as methyl or ethyl alcohol, a great enough some of the -residual acetate groups water'nolutionoi an alkali or alkaline salt, such of the resin will .be converted to alcohol groups, as sodium or potassium hydroxide or carbonate, 40 which tends 'to stiflen the resin and is desirable ccntainlnglan acohol concentration, preferably, in some cases, especially where the acetal resin equivalent to that .0! theresin solution is added a a n y be 80- Th amountoi alkali to the aresinsolution. Thecuantity or alkali or 1 used be varied accordingly. The surplus alkaline salt added should be slightly in excess liquid then is drained from the precipitated resin or that required to neutralize the mineral acid and the resin washed with water to remove alkali catalyst. The resin solution may be filtered either or any free salts, 1 before or after treatment toremove dirt or other 1 Thethird major step is the stabilization with ioreign substance. After the addition oi the neu I methanol. After washing, the resin is given a trallzing agent the resin is then precipitated from i final stabilization treatment by .ubiecting it to the solution. preferably, by diluting the solution. 5

the action of methanol, with which may in some cases'be used tri-ethanol-amine or other amino body oi! basic characteristic, in a water suspension which may contain an alkali, such as sodium or potassium hydroxide or carbonate.

cipitated resin. The precipitated resin is put in 5 The resin should be flnely divided so the staa reasonable time. A slight rise in temperature also facilitates" this peneration. Suitable proportions by weight are:

(a) "Resi 100 Water 400 Methanol--- 5 0 I (b) Resi 100 Water 400 Metha 40 Tri-ethanol-amine 0.1

(c) Res 100 Water 400 Methanol 40- Potassium hydroxide 0.1

The resin is then centrifuged. The centrifuged product will ordinarily contain residual methyl alcohol from 2 to 10% and less than 0.01% of tri-ethanol-amine, if used, and less than 0.05% of alkali salts. The resin then is dried at a temperature of 50 to 80 C., but a temperature of 100 C. or even higher may be used. While methanol appears to give the most satisfactory results it will be understood that other lower aliphatic alcohols may be advantageously employed.

The best results are obtained by employing each of the three major steps, namely, neutralization in solution, neutralization in suspension, and treatment with methanol. I find that the methanol treatment combined with neutralization in solution produces a certain definite improvement in stability, while neutralization in suspension followed by methanol treatment gives a satisfactory product 'only when the particle size is small, about 60 mesh. Neutralization in solution .bilization mixture can penetrate the resin within products which are either stable or soluble, or I are volatile. It is also possible that uncombined aldehydes may be a cause of instability and that theyreact with methanol in presence of traces of a mineral acid to-produce compounds which are stable, soluble or volatile. r

Treatment in accordance with the invention ,eifects an improvement ingthe stability of the resin regardless of the method used in the manufacture of the resin. However, the best results are obtained by treating resins which have been carefully prepared in accordance with the best practice known in the art. Thus, it is well known in the art that in acetalization with the higher aliphatic aldehyde's, the use of too high temperature, for example, 80 C., or heating for too long a time, for example, for more than eight hours, 7

or the use of too large a quantity of catalyst in acetalization, such as more than 2 per cent of the weight of the total reaction mixture, tend to produce discolored resins. The use of an excess of aldehyde which will remain unreacted should be avoided or the excess removed. Care should be exercised to avoid all such known faulty the invention if maximum stability is desired. The present application is a continuation of my "prior application, Serial No. 122,575, filed Janufollowed by neutralization in suspension produces a certain improvement in stability also while neutralization in suspension alone generally has been found unsatisfactory unless the resin is secured with a very fine particle size, about 80 mesh or finer. In general, a fine particle size is desirable to facilitate stabilization.

While the exact nature of the reactions which take place when the resin is treated in accordance with my invention is somewhat uncertain, nevertheless, the great improvement in stability of the resin produced has been demonstrated by severe tests. For instance, I have found that if five grams of the resin in the form of fine particles is placed in a U shaped tube of diameter and air is passed through the tube at the rate of four liters per hour while the resin is heated at a temperature of 150 0., there is no appreciable change in color or in solubility characteristics at the end of four hours. On the other hand, the best resins now available and which are believed to be made either by the process described in the Morrison Patent No. 2,036,092 or in French Patent No. 792,661 when given the same test darken to light brown in the case of formaldehyde resins, and dark brown in the case of butyraldehyde resins before the end of four hours.

It is possible that the residual catalyst in the unstabilized resin, or foreign substances included in the raw materials from which the resins are prepared produces unstable decomposition products. Stabilizing treatment undoubtedly removes minute residuums of the acid catalyst. It is also possible that alkyl sulfates or halides are formed in the resin solution and the resin itself and that these are causes of instability. The methanol may combine with such compounds to form ary 27, 1937.

I claim: 1. The method of stabilizing a. vinyl acetal resin formed in the presence of a mineral acid catalyst which includes the steps comprising subjecting a solution of the resin to the action of a neutralizing agent for the acid catalyst, subjecting a suspension of theresin to the action of .a neutralizing agent for the acid catalyst, and

subjecting a suspension of the resin to the action of methanol.

2. The method of stabilizing a vinyl acetal resin formed in the presence of a mineral acid catalyst which includes the steps comprising subjecting a solution of the resin to the action of a neutralizing agent for the acid catalyst, and subjecting a suspension of the resin to the action of a neutralizing agent for the acid catalyst.

3. The method of stabilizing a vinyl acetai resin formed in the presence of a mineral acid catalyst which includes the steps comprising subjecting a solution of the resin to theaction of a neutralizing agent for the acid catalyst, and

subjecting a suspension of the resin to the action of methanol.

4. The method of stabilizing a vinyl acetai resin formed in the presence of a mineral acid catalyst which includes the steps comprising subletting a suspension of the resin to the action of a neutralizing agent for the acid catalyst, and subjecting a suspension of the resin to the action of methanol.

5. The method of stabilizing a vinyl .acetal resin formed in the presence of a mineral acid 7. That step in the production or a stable polyvinyl acetal resin produced by the action of an acid catalyst which comprises subjecting the acid-free resin while in suspension to the action 01 methanol. I

8. The method of stabilizing a vinyl acetal resin formed in the presence or a mineral acid catalyst which includes the steps comprising subjecting a solution of the resin to the action of a neutralizing agent for the acid catalyst, subjecting a suspensionoithe resin to the action of a neutralizing agent for the acid catalyst, and sub- 1 jecting a suspension of the resin to the action of a lower aliphaticalcohol.

9.1 The method of stabilizing a vinyl acetal resin formed in the presence of a mineral acid catalyst which includes the steps comprising subcatalyst which includes the steps comprising sub- Jecting a suspension or the resin to the combined action of a lower aliphatic alcohol and a neutralizing agent for the acid catalyst.

-12. That step in the production oi a stable polyvinyl acetal resin produced by the action of an acid catalyst which comprises subjecting the acid-treeresin while in suspension to the action oi a lower aliphatic alcohol.

13. The method of stabilizing a vinyl acetal resin formed in the presence of a mineral acid catalyst which includes the steps comprising subjecting a suspension of the resin to the combined action of ethanol and a neutralizing agent for the acid catalyst. i p

14. The method of stabilizing a vinyl acetal resin formed in thepresence. of a mineral acid resin formed in the presence of a mineral acid 30 catalyst which includes the .step comprising subjecting a suspension of the resin to the combined action of a lower aliphatic alcohol and an inorganic alkaline neutralizing agent for the acid jecting a suspension of the resin to the combined action 0! ethanol and an inorganic alkaline neutralizing agent for the acid catalyst.

JOSEPH DAHLE. 

